Krishna
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Step 1: Remember the Formula to calculate radius R of the circumscibed circle an isosceles triangle

            NOTE: Radius R of the circumscibed circle an isosceles triangle of base b    

                        and lateral side a are given by 

                             R = \frac{a^2}{\sqrt{4a^2 - b^2}}


Step 2: Find the relationship between h, b and a (Pythagoras in triangle) 

            NOTE: Divide the Isosceles triangles into two right triangles.

                       a^2 = (\frac{b}{2})^2 + h^2


Step 3: Rewrite the relation in height

                       4h^2 = 4a^2 - b^2


Step 4: Replace  4 a^2 - b^2  by 4 h^2 in the

            formula for R 

           R = \frac{a^2}{\sqrt{4 h^2}}


Step 5: Find the base of the triangle by substituting the known values in the above equation.

            NOTE: R = \frac{a^2}{\sqrt{4 h^2}}

                         R * \sqrt{4 h^2} = a^2

                      Height h = 16 cm and Radius R = 9 cm

                       \sqrt{4 * (16)^2} * 9 = a^2

                       2* 16 * 9 = a^2

                       a = 12\sqrt{2}

                        

Step 6: Substitute the base (a) value in the formula for the lateral side.